Process for producing alkali chlorate or alkali perchlorate



G. J. CRANE PROCESS FOR PRODUCING ALKALI CHLORATE OR ALKALI PERCHLORATEOct. 31, 1967 2 SheetsSheet 1 Original Filed April 27, 1964 3,350,286PROCESS FOR PRODUCING ALKALI CHLORATE OR ALKALI PERCHLORATE OriginalFiled April 27, 1964 v G. J. CRANE Oct. 31, 1967 2 Sheets-Sheet 2 FIG. 2Z

United States Patent 3,350,286 PROCESS FOR PRODUCING ALKALI CI-ILORATE0R ALKALI PERCHLORATE George J. Crane, Islington, Ontario, Canada,assignor to Huron Nassau Limited, Nassau, Bahama Islands, a corporationof The Bahama Islands Continuation of application Ser. No. 362,719, Apr.27, 1964. This application Jan. 23, 1967, Ser. No. 611,173 Claimspriority, application Canada, Nov. 5, 1963, 888,375 3 Claims. (Cl.20495) This application is a continuation of Ser. No. 362,719, filedApr. 27, 1964, which is now abandoned.

This invention relates to an improved process of manufacturing alkalichlorates and perchlorates by means of multipolar electrolytic cells.

The most economic manufacture of sodium chlorate and perchlorate isusually performed in multipolar electrolytic cells. These cells comprisea series of parallel electrodes mounted in a box and sealed at theiredges and bottom to prevent leakage of solution or electric current, thesolution to be electrolyzed being maintained between each set ofelectrodes. A brine such as NaCl is electrolyzed in the cells through anumber of intermediate reactions to form the sodium chlorate, withhydrogen gas evolved as a by-product when oxygen from the water is freedto enter into the reaction. The overall chemical reaction is representedby 3H O+NaCl NaClO -|-3H The brine solution containing NaCl and someNaClO circulates between the electrodes and at each pass some of theNaCl is converted to NaClO Fresh solution enters each electrodecompartment at the lower edge of the electrode through an inlet pipe,and the natural circulation of the liquor between the electrodes iscaused by the generation of hydrogen gas between the cell plates. Thisreduces the average specific gravity of the material between theelectrodes. The heavier dense fresh liquor from the tank enters into thebottom inlet pipes and forces out the mixture of liquid and gas throughupper pipes positioned at the top of the electrodes. In addition a minorcirculation force is caused by a temperature increase of the electrolytein the cells between the electrodes.

The efiiciency of the electrolysis and overall operating economy issensitive to a number of operating conditions such as temperature, pH,uneven flow rate of electrolyte, bubble formation and variations inspecific gravity of the liquid gas material between the electrodes.Also, under poor circulation conditions hydrogen bubbles produce a frothat the surface of the electrolyte which further interferes with the freedischarge of the solution from the effluent pipes. In addition thisfroth constitutes an explosive hazard. Maintaining a sufficiently largeflow rate necessitates increasing the diameter of the inlet and effluentpipes but this consequently increases the current leakage. For maximumefliciency it is desirable to independently vary the flow rate of theelectrolyte between the electrodes to compensate for the increasingspace between the electrodes as they Wear away, and also variations inthe electrode surface. In addition changes in the chemical nature of theelectrolyte and changes in current density require independent variationfor the flow rate.

It is an object of the invention to control the conditions of theelectrolyte between the electrodes.

It is a further object of this invention to decrease stray currentlosses.

Other objects of this invention will be made apparent from thedescription to follow.

The objects of this invention are attained in a process for theproduction of compounds selected from the group 3,350,286 Patented Oct.31, 1967 ice consisting of alkali chlorates and alkali perchlorates bythe electrolysis of an alkali chloride brine which comprises:electrolyzing said brine in a multipolar electrolytic cell, providinginlet and outlet means for said cell, pumping fresh electrolyte into theinlet means of said cell at a positive and controlled pressure, andremoving electrolyzed solution from the outlet means.

The invention is more suitably understood by reference to the diagramsin which:

FIGUREI is a perspective view of a multipolar cell;

FIGURE 2 is a perspective view of a multipolar cell bearing constantpressure means; and I FIGURE 3 is a perspective view of a multipolarcell positioned in a tank.

In the drawings a typical cell of the prior art type is shown in FIGURE1 having an outer wall 1, monopolar electrodes 2, and multipolarintermediate electrodes 3. The multipolar electrodes are sealed intogrooves in the side wall to form individual and separate compartments 5.Adjacent cell compartments are separated from each other by insulatingelements 4. Inlet pipes 9 and outlet pipes 8 provide a path for freshbrine to enter the electrolyzed brine to leave the cell. The cell box isplaced in a large tank to a depth below the inside level of liquor inthe tank shown at 7. In normal operating conditions a normal insidelevel will be as shown at 6. This diflference in hydrostatic levelsbetween 6 and 7 will produce the outflow of liquor from the cell box.

One form of the inventive feature of this apparatus is shown in FIGURE 2in which manifolds 11 are shown surrounding each set of inlet tubes.This is more completely illustrated in FIGURE 3 in which the cell isshown in a normal operating condition placed in a large tank. Freshelectrolyte from the tank is supplied through pipe 13 by pump 12 intopipes 10 and then to manifolds 11 surounding the inlet pipes 9. A valve14 regulates the amount of electrolyte which may be forced through thesystem. Only two monopolar electrodes are shown in FIGURE 1 but moreparallel circuits may be assembled in the cell box in which case thenumber of monopolar electrodes must be increased. Only four cellcompartments are shown in series but this number can be increased tofifty or greater depending on the total voltage available. The inlettubes 9 not only distribute fresh electrolyte evenly across the entirewidth of the cell but they also have a greater resistance to leakage ofelectric current than tubes usual for this type of circulation. This isbecause their length can be increased and the diameter decreased, thegreater resistance to flow of liquid being compensated for by pump 12.

By maintaining a positive circulation of electrolyte in theinterelectrode space the semi stationary foam that forms with certainliquid electrolyte compositions is eliminated. In addition a moreuniform consumption of the graphite electrodes is attained due to thereduced temperature, denser uniform electrolyte mixture, moreelectrolyte conductivity and even laminar flow between the electrodes.Furthermore the concentration of unwanted by-products is reduced thuslessening the loss of chemicals through gaseous intermediates.Consequently, the output of a given size of electrolyti multipolar cellmay be significantly increased with only a small expenditure of capital.

Iclaim:

1. A process for the production of compounds selected from the groupconsisting of an alkali chlorate and alkali perchlorate by theelectrolysis of an alkali chloride brine comprising electrolyzing saidbrine in a multipolar electrolytic cell consisting of a plurality ofspaced multipolar electrodes dividing said cell into a plurality ofcompartments having insulating means separating adjacent compartments,each of said compartments being rovided with inlet conduit meansadjacent the bottom thereof, each of said inlet conduit means openingintermediate spaced opposed electrode faces, and with outlet conduitmeans adjacent the top thereof, each said outlet conduit meansdischarging intermediate said spaced electrode faces, introducingelectrolyte through said inlet conduit means through manifold means intothe space between said electrode faces thereby evenly distributing saidelectrolyte throughout the lower portion of each compartment,withdrawing electrolyzed material and maintaining a positive pressure onthe electrolyte introduced through said inlet conduit means by a pumpconnected to said manifold means.

2. The process of claim 1 including containing said cell in a tankprovided with electrolyte, maintaining the level of electrolyte in saidtank at a depth below the outlet conduit means of said cell whereby thehydrostatic level within said cell produces an outflow of electrolyteReferences Cited UNITED STATES PATENTS 718,249 1/1903 Haas 2042682,350,669 6/1944 Boller 204237 FOREIGN PATENTS 531,803 1/1941 GreatBritain.

JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner.

1. A PROCESS FOR THE PRODUCTION OF COMPOUNDS SELECTED FROM THE GROUPCONSISTING OF AN ALKALI CHLORATE AND ALKALI PERCHLORATE BY THEELECTROLYSIS OF AN ALKALI CHLORIDE BRINE COMPRISING ELECTROLYZING SAIDBRINE IN A MULTIPOLAR ELECTROLYTIC CELL CONSISTING OF A PLURALITY OFSPACED MULTIPOLAR ELECTRODES DIVIDING SAID CELL INTO A PLURALITY OFCOMPARTMENTS HAVING INSULATING MEANS SEPARATING ADJACENT COMPARTMENTS,EACH OF SAID COMPARTMENTS BEING PROVIDED WITH INLET CONDUIT MEANSADJACENT THE BOTTOM THEREOF, EACH OF SAID INLET CONDUIT MEANS OPENINGINTERMEDIATE SPACED OPPOSED ELECTRODE FACES, AND WITH OUTLET CONDUITMEANS ADJACENT THE TOP THEREOF, EACH SAID OUTLET CONDUIT MEANSDISCHARGING INTERMEDIATE SAID SPACED ELECTRODE FACES, INTRODUCINGELECTROLYTE THROUGH SAID INLET CONDUIT MEANS THROUGH MANIFOLD MEANS INTOTHE SPACE BETWEEN SAID ELECTRODE FACES THEREBY EVENLY DISTRIBUTING